Process of final passivation of an integrated circuit device

ABSTRACT

A process for forming a final passivation layer over an integrated circuit comprises a step of forming, over a surface of the integrated circuit, a protective film by means of High-Density Plasma Chemical Vapor Deposition.

TECHNICAL FIELD

[0001] The present invention relates to a process of forming finalpassivation of an integrated circuit device and a device made by saidprocess.

BACKGROUND OF THE INVENTION

[0002] Semiconductor integrated circuits manufactured with Large Scaleof Integration (LSI) technologies (LSI, VLSI, ULSI) require a protectivelayer against mechanical stress and aggressive chemical agents. Thislayer, generally called “passivation layer” is typically formed bysilicon-based dielectrics, such as silicon dioxide (USG),phosphorus-doped or fluorurate-doped silicon oxide (PSG or FSG), siliconnitrides and nitride oxides (Si₃N₄, SiO_(x)N).

[0003] The passivation layer is conventionally formed by means ofChemical Vapor Deposition (CVD) techniques, either Plasma-Enhanced(PECVD) or at Atmospheric Pressure (APCVD).

[0004] Final passivation layers formed by means of the above-referredconventional techniques have up to now proved to be sufficientlysatisfactory, and in view of the relatively low cost of both PECVD andAPCVD manufacturing equipment their use has never been disputed.

[0005] On the other hand, a new CVD technique has been known for someyears for the formation of Inter-Metal Dielectric (IMD) protective filmsin ULSI circuits. Such a technique, called High-Density Plasma CVD(HDPCVD), is substantially a combination of two simultaneous processes,i.e., deposition and sputtering.

[0006] The advantage of HDPCVD over known alternative IMD film formationprocesses (such as PECVD, APCVD or Spin-On-Glass (SOG) processes) isthat this technique allows for better (complete) filling of gaps betweenmetal lines, even for sub-micrometric intra-metal line distances, of theintegrated circuit.

SUMMARY OF THE INVENTION

[0007] To resolve the difficulties of conventional techniques, an objectof the present invention is to provide a new process of finalpassivation of integrated circuits by means of which final passivationlayers having improved characteristics over conventionally-formedpassivation layers can be formed, particularly suitable where the scaleof integration of the integrated circuits is increased.

[0008] One embodiment of the present invention includes a method forforming a final passivation layer over an integrated circuit,characterized by comprising a step of forming, over a surface of theintegrated circuit, a protective film by means of High-Density PlasmaChemical Vapor Deposition technique.

[0009] By applying the present invention, it is possible to formpassivation layers with improved step coverage characteristics, even forextremely small geometries, for the integrated circuits. The resultingpassivation layer of the integrated circuit does not depend, forexample, on the distance between the metal lines of an upper metal layerof the integrated circuit even if such a distance is as low asapproximately 0.2 μm. Additionally, the gaps between said metal linesare completely filled by the passivation layer.

[0010] Said protective film can be made of silicon dioxide,phosphorus-doped or fluorurate-doped silicon oxide, silicon nitrides oroxinitrides, and other suitable materials having a low dielectricconstant.

[0011] The passivation layer may further comprise other films inaddition to the one formed by means of HDPCVD. For example, these otherfilms may be formed by means of PECVD or APCVD techniques. In this case,a first passivation film is formed over the surface of the integratedcircuit to be protected by means of HDPCVD, thus filling completely thegaps between the metal lines defined in the uppermost metal layer of theintegrated circuit. Over said first film, other passivation films areformed by means of conventional PECVD or APCVD techniques.

[0012] It has been realized and practically verified by Applicant that,notwithstanding the present common technical prejudice in favor ofPECVD- or APCVD-formed final passivation layers, the conventional PECVDor APCVD techniques could no longer provide satisfactory results as theintegration scale of integrated devices is increased and the presentinvention provides considerable advantages.

[0013] The features and advantages of the present invention will be madeapparent from the following detailed description of a particularembodiment thereof, illustrated as a non-limiting example in annexeddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a schematic cross-sectional view of a portion of anintegrated circuit before the formation of the final passivation layer.

[0015]FIG. 2 shows the portion of integrated circuit of FIG. 1, after afinal passivation layer has been formed by means of a process accordingto the invention.

[0016]FIG. 3 shows an additional layer deposited over the passivationlayer according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0017] In FIG. 1, a portion of an integrated circuit chip 3 isschematically shown in cross-section. The chip 3 generically comprises asubstrate 4, over which, e.g., metal lines 2 are formed and between themetal lines 2, gaps 1 are formed. If the integrated circuit isfabricated by means of an Ultra Large Scale of Integration (ULSI)process, the gaps 1 can be as narrow as approximately 0.2 μm.

[0018] The integrated circuit chip 3 is to be protected by means of afinal passivation layer.

[0019] According to an embodiment of the present invention, said finalpassivation layer is a dielectric layer of undoped silicon dioxidedeposited over the surface of the integrated circuit chip 3 by means ofHigh Density Plasma Chemical Vapor Deposition (HDPCVD). The chip(actually, the whole semiconductor wafer to which the chip belongs) isintroduced in a CVD reaction chamber wherein the following processconditions are preferably provided:

[0020] O₂, SiH₄, Ar gas flow between 5-150 sccm, for each gas;

[0021] 2000 to 4000 W source Radio-Frequency (RF) power;

[0022] a reaction chamber pressure of less than 10 mTorr; and

[0023] a 2.5:1 to 8.0:1 deposition/sputtering ratio.

[0024] At the end of this process, a passivation layer 5 covers theintegrated circuit, as schematically shown in FIG. 2. It is to be notedthat the passivation layer 5 completely fills the gaps 1 between themetal lines, even if such gaps are as narrow as approximately 0.2 μm.

[0025] Even if the above example has been referred to the formation of asilicon dioxide passivation layer, other materials, for example,phosphorus-doped or fluorurate-doped silicon oxide (PSG or FSG), siliconnitrides and nitride oxides (Si₃N₄, SiO_(x)N_(y)) can as well bedeposited by means of HDPCVD.

[0026] In an alternative embodiment, the passivation layer could alsocomprise a stack of layers, the lowermost formed by means of HDPCVDtechnique, and the superimposed layers may be formed by conventionalPECVD or APCVD techniques. In FIG. 3, an additional layer 6 formed byPECVD or APCVD is shown being superimposed over the passivation layer 5.In this way, the lowermost, HDPCVD deposited layer allows for a completefilling of the gaps.

[0027] From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

What is claimed is:
 1. A method for forming a final passivation layerover an integrated circuit, the method comprising a step of forming,over a surface of the integrated circuit, a first protective film bymeans of High-Density Plasma Chemical Vapor Deposition.
 2. The method ofclaim 1 wherein said High-Density Plasma Chemical Vapor Depositioncomprises the following steps: placing the integrated circuit into areaction chamber; providing a mixture of a dielectric material gas andan inert gas with a gas flow in between 5 to 150 sccm within thereaction chamber, for each gas; providing a radio-frequency source ofpower at about 2000 to about 4000 watts within the reaction chamber;providing a reaction chamber pressure of less than 10 mTorr; anddepositing the passivation layer at a deposition/sputtering ratio ofabout 2.5:1 to about 8.0:1 to the integrated circuit.
 3. The method ofclaim 2 wherein said dielectric material gas includes oxygen, or siliconhydride, or phosphorus, or fluorine, or nitrogen, or any combinationthereof.
 4. The method of claim 2 wherein said inert gas includes argon.5. The method of claim 1, further comprising a step of providing asecond protective film over said first protective film.
 6. The method ofclaim 5 wherein said second protective film is formed by Plasma-EnhancedChemical Vapor Deposition (PECVD) or by Atmospheric Pressure ChemicalVapor Deposition (APCVD).
 7. An integrated circuit device, comprising apassivation layer having a first dielectric film deposited by means ofHigh-Density Plasma Chemical Vapor Deposition.
 8. The device of claim 7,further comprising a second dielectric film deposited over the firstdielectric film and formed by Plasma-Enhanced CVD or by AtmosphericPressure CVD.
 9. A method for forming a final passivation layer having afirst protective film over an integrated circuit, the method comprising:placing an integrated circuit into a reaction chamber; providing amixture of a dielectric material gas and an inert gas within thereaction chamber; providing a radio-frequency source of power at about2000 to about 4000 watts within the reaction chamber; providing areaction chamber pressure of less than 10 mTorr; and depositing thefirst protective film of the passivation layer at adeposition/sputtering ratio of about 2.5:1 to about 8.0:1 to theintegrated circuit.
 10. The method of claim 9 wherein the dielectricmaterial gas includes oxygen, or silicon hydride, or phosphorus, orfluorine, or nitrogen, or any combination thereof.
 11. The method ofclaim 9 wherein said inert gas includes argon.
 12. The method of claim9, further comprising a step of providing a second protective film oversaid first protective film.